1. Field of the Invention
The present invention relates to an optical disk recording and playback device that is capable of recording a signal and forming a visible image on an optical disk by means of laser light applied from a laser diode provided in an optical pickup.
2. Description of the Related Art
In recent years, optical disk recording and playback devices for use with optical disks that are called DVDs (digital versatile disks) have become widely available. Such an optical disk recording and playback device is configured to be capable of being used not only with DVDs but also with CDs (compact disks). An optical pickup provided in such an optical disk recording and playback device capable of being used with both types of disk includes two types of laser diode that emit two different wavelengths of light, one of which emits laser light having a suitable wavelength for the recording density of DVDs, and the other of which emits laser light having a suitable wavelength for the recording density of CDs. Switching between the laser diodes is performed in accordance with the type of optical disk in use.
Transparent substrates of a DVD and a CD have significantly different thicknesses of 0.6 mm and 1.2 mm, respectively, as measured from a surface to a signal recording layer. For this reason, in a DVD and CD compatible optical pickup, different NAs (numerical apertures) are required of an objective lens to achieve suitable optical properties for the respective types of disks. When a single objective lens is to be used for both DVDs and CDs, a desired optical pickup can be achieved by employing an objective lens configured to provide different NAs with respect to the respective wavelengths of laser light that are suitable for the respective types of disk.
When a signal is recorded on a disk using an optical disk recording and playback device, in order to identify the content of the signal recorded on the disk, after completion of a signal recording operation, some users place, on a surface opposite to a signal recording surface of the disk, a label or the like having information of the recorded content printed thereon, for example, song titles, when music is recorded, while other users write song titles or the like on the non-recording surface using a felt-tipped pen or the like.
However, there are some problems in that such methods including a step of placing a label or the like on a disk surface or of writing song titles or the like on a disk surface are inconvenient and can adversely affect the playback operation of the signal recorded on the disk. As a method to overcome such problems, a technique for forming a visible image on a photosensitive surface of an optical disk by means of laser light applied from an optical pickup has been developed.
However, currently known techniques remain problematic in that because a visible image is formed on a signal surface on which a data signal is recorded, when the recording capacity for data signals is large, the area for forming a visible image is reduced and it is usually impossible to display information sufficient to identify all recorded data. On the other hand, when the formation/recording of a visible image on an optical disk is performed on a surface opposite to the signal recording surface of the disk, there is another problem in that users must inconveniently turn the disk upside down after completion of a recording operation of data onto the disk.